Learning Forum

[Zwernjayden]

I am trying to model atomizing impinging streams for a rocket combustion case. The DPM streams are clearly impinging, and collision+breakup occurs, but the center two jets dont seem to be impacted very much. Is there a way I can get a better transfer of momentum between particles? I tried increasing the time step, but it got to the point where it became computationally too expensive for my model. Is this a case where I should use vof to dpm transition?

[Rob]

Are all injections the same droplet material? 

[Zwernjayden]

No two are multicomponent ethanol and water, the center two are Lox droplets. That shouldn't matter though right?

[Rob]

It does - read how the collision model works. 

[Zwernjayden]

I read through manual and didn't see anything saying they had to be the same. In addition, there is another forum post I saw that determined collision is possible between unlike droplets but coalescence is not

[Rob]

I'll need to recheck - I would tend to look at a collision models as likely to need other approaches. But, if a collision occurs it's a function of cell and parcel count: so if the cells are small you may find the collision maths isn't triggered. 

[Zwernjayden]

Ok thank you. I know collision works because if I turn off collision, no breakup occurs at all and the streams just clip right through eachother and hit the wall. Ill try the vof-dmp transition maybe

[Rob]

Check your cell sizes, and whether the problem is repeated if all injections use the same material mixture.